This invention relates generally to kiln firing of ceramic ware. More specifically the invention is directed to support or setter devices for the ware when it is disposed within a kiln during the firing operation.
In the firing of ceramic and glass-ceramic articles having a glaze composition applied thereto, it is conventional to utilize supports therefore composed of a refractory material. Such techniques are used in the present day practice employed in the manufacture of glazed dinner ware and involves supporting the ware, after being dipped in unfused glaze, on a plural point support provided by refractory elements of different shapes, such as upright pins, tetrahedrons or spheres.
One of the problems of firing the glaze upon the outer surface of the ware is the adherence between the glaze and the support with consequent pitting of the glazed surface at those points of contact between the ware and support. Such pits extend through the glazed surface and appear as dark spots during subsequent use of the ware. Depending upon the nature of the support, portions thereof may tend to adhere to the ware and to sever from the support. These portions must be ground from the surface of the ware.
The refractory setter device for supporting glazed ceramic ware during firing within a kiln should ideally demonstrate four characteristics. Certainly it must be capable of withstanding the high temperatures required for glazing. The setter material must exhibit good resistence to thermal shock so that degradation through cracking and spalling is not encountered. This material must not react chemically with the glaze or the clay body of the article being fired. Finally, the material of which the setter is made must not be wetted by the glaze such that a glaze-to-glaze bond will create sticking between the ceramic ware article and the refractory setter device.
In the prior art, U.S. Pat. Nos. 3,266,162 to Rush; 3,782,981 to Rostoker and 3,948,594 to Irwin, Jr. are illustrative of several present day practices employed in supporting ware during firing operations. However, in using the proposals suggested in the prior art, some drawbacks or disadvantages have been encountered. As the glaze fuses during the firing operation, it wil run and fuse to the support pins or elements that are acting to support the ware, thus requiring the pins or elements in some cases to be broken away or otherwise removed from the ware after it is removed from the kiln. Often fragments of the refractory material of which the setter device is constructed are left fused into the glaze and must be ground away or dressed.